1. Field of the Invention
This invention relates to an image displaying method for a head-mounted type display unit (HMD: Head Mounted Display).
2. Description of the Related Art
A virtual image display apparatus for allowing an observer to observe a two-dimensional image formed by an image forming apparatus as an enlarged virtual image by means of a virtual image optical system is known and disclosed, for example, in Japanese Patent Laid-Open No. 2006-162767 (referred to as Patent Document 1 hereinafter).
FIG. 1 schematically shows the image display apparatus mentioned above. Referring to FIG. 1, the image display apparatus 100 shown includes an image forming apparatus 111 including a plurality of pixels arrayed in a two-dimensional matrix, a collimate optical system 112 for converting light outputted from the pixels of the image forming apparatus 111 into parallel light, and an optical apparatus or a light guide section 120 to which the parallel light from the collimate optical system 112 is inputted and by and from which the parallel light is guided and outputted. The optical apparatus 120 includes a light guide plate 121 in which light inputted thereto propagates by total reflection until it is outputted therefrom, and first deflection section 130 formed, for example, from a light reflecting film of one layer for reflecting the light inputted to the light guide plate 121 so that the light inputted to the light guide plate 121 may be totally reflected in the inside of the 121 light guide plate 121. The optical apparatus 120 further includes a second deflection section 140 formed, for example, from a light reflecting multilayer film having a multilayer lamination structure for emitting the light propagated in the inside of the light guide plate 121 by total reflection from the light guide plate 121. Such an image display apparatus 100 as just described can achieve, if it is used to configure a head-mounted display unit, reduction in weight and size of the apparatus.
Another virtual image display apparatus which uses a hologram diffraction grating in order to allow an observer to observe a two-dimensional image formed by an image forming apparatus as an enlarged virtual image by means of a virtual image optical system is known and disclosed, for example, in Japanese Patent Laid-Open No. 2007-94175 (referred to as Patent Document 2 hereinafter).
FIGS. 15A and 15B schematically shows a concept of the image display apparatus mentioned above. Referring to FIGS. 15A and 15B, the image display apparatus 300 shown basically includes an image forming apparatus 111 for displaying an image, a collimate optical system 112, and an optical apparatus or a light guide section 320 for receiving the light displayed on the image forming apparatus 111 and guiding the light to the pupil 41 of an observer. The optical apparatus 320 includes a light guide plate 321, and a first diffraction grating member 330 and a second diffraction grating member 340 provided on the light guide plate 321 and each formed from a reflection type volume hologram diffraction grating. Light emitted from pixels of the image forming apparatus 111 is inputted to the collimate optical system 112, and parallel light is produced by the collimate optical system 112 and inputted to the light guide plate 321. The parallel light is inputted to a first face 322 of the light guide plate 321 and outputted from the first face 322. Meanwhile, the first diffraction grating member 330 and the second diffraction grating member 340 are attached to a second face 323 of the light guide plate 321 which extends in parallel to the first face 322 of the light guide plate 321.
Meanwhile, a subtitle display apparatus for the subtitle display for which a head-mounted type display unit is used and which is mounted immediately in front of a spectator by a mounting section to assist watching of a theatrical performance is known and disclosed, for example, in Japanese Patent Laid-Open No. 2002-018158 (referred to as Patent Document 3 hereinafter). The subtitle display apparatus disclosed in the document mentioned includes an information outputting section for producing and storing original information for the subtitle display and outputting the original information as subtitle information, and a signal transmission section for transmitting the subtitle information in a superimposed relationship on a signal transmission medium. The subtitle display apparatus further includes a signal reception section for extracting the subtitle information from the signal transmission medium and outputting the subtitle information, and a subtitle display section disposed immediately in front of a spectator for displaying subtitles based on the subtitle information.